Mola mola

I wrote a few weeks ago about how massive numbers of Velella^2 just won't stop washing up on the west coast, really taking all the cache out of these animals. They're just not a rare enough sighting any more to constitute a hipster-find. But the plus side is that we get to see things like this happening. Jodi Frediani captured several pictures of this goggly-eyed prehistoric force of nature in Monterey Bay.

It turns out that people just assume(2)Mola mola are supposed to eat larger jellies(3) but their diet is pretty poorly understood, there really isn't very much quantitative data. Other animals that preferentially eat large jellies have mouths that are much better suited for it (Figure 2) and there is increasing speculation that they are much less picky eaters(4). I love how difficult these pictures make it look to catch a barely mobile floating jelly blob. These Velella must be worth it somehow. Maybe the Mola likes the crunchy sail bit - they're like potato chips.

This species is so endearing because it's huge and clumsy at swimming. In fact, when I was an undergrad, I was taught this was the largest species of plankton(5), but again, we are learning more that they are actually pretty swell swimmers, thankyouverymuch. I recall being on a whale watch and seeing one breach (the sunfish - we didn't see any dang whales on the whale watch). The weird shape of the fish (Figure 3) is apparently the likely result of adapting to life in the open ocean when you start out looking something like a pufferfish (Figure 4, and reference 4). The dorsal and anal fins are used for propulsion, which you can see really well in this video, and the tail has receded into a mere rudder (called a clavus).

...ocean sunfish stroke their dorsal and anal fins synchronously...to generate a lift-based thrust that was likened to the symmetrical flipper beats of penguins. Essentially, M. mola uses its dorsal and anal fins as a pair of wings. It is worth noting that this is the only animal known to use two fins for this purpose that are not originally bilaterally symmetrical. (5)

It is worth noting indeed - you go M. mola.

Figure 3. Super weird skeleton of a super weird fish. Notice how the vertebrae are nearly degenerated, but some of the spinal processes are really well integrated with the bones stabilizing the dorsal fin.

Lastly: behavior, because what good is a weird-looking animal if it acts totally normal?

In addition to swimming all funny, and breaching (possibly to dislodge parasites), these fish sunbathe (possibly(6) to warm up after deep dives). Other nutso facts:

The most fecund fish, no, the most fecund vertebrate on the planet! Releasing an estimated 300 MILLION eggs per season.

Their larvae retain spines that not only look super punk, but are shared with pufferfishes they are related to (Figure 4)

Figure 4. Larval punkfish. If this isn't a Pokemon character by now, I don't know what to think any more. Photo: G. David Johnson

The result of all of this weirdness is entirely hypnotic to watch. Hypnotic isn't even the right word, it's more like disorienting. If you ever get a chance to go see them at the Monterey Bay Aquarium, or, god forbid, in their actual habitat(7), you will truly feel like an alien on your own planet. As in, how could I be on this planet so long and not know anything about anything?

References and Miscellany

(1) I still can't resolve whether it should be tautonomical or tautonymical, it's driving me kind of nuts. Don't I wish I had majored in linguistics?(2) And you know what they say about assuming...(3) To play the pedant here, Velella are technically not jellies. True jellyfish are Scyphozoans while Velella are hydrozoans, but I don't want to steal the limelight from the vertebrate star here!(4) Pope et al. 2010 Rev Fish Biol Fisheries(5) Plankton in the strict sense, means "drifter", those at the mercy of the currents(6) Noticing a theme here with all the "possibly"s? The field is wide open!(7) If this is your jam, do it soon. These fish face substantial mortality as bycatch in gill nets etc. Though the population is thought to be relatively stable - I again refer you to the number of qualifying "possibly"s in this post, meaning we don't know as much as we think we do.